Method of fabricating tissue



Dec. 26, 1961 H. F. DONNELLY 3,014,832

. METHOD OF FABRICATING TISSUE Filed Feb. 12, 1957 INVENTOR.

HMJD

3,614,832 METHOD OF FABMCATWG TISSUE Harold F. Donnelly, Appleton, Wis,assignor to Kimberly-Clark Corporation, Neenah, Wis, a corporation ofDelaware Filed Feb. 12, 1957, Ser. No. 639,791 2 Ciaims. (Cl. 162-111)This invention generally relates to a method of fabricating improvedtissue. The invention more particularly relates to a method ofmanufacturing dry creped cellulosic tissue webs having improvedcharacteristics and physical properties.

In the manufacture of dry creped tissue webs by conventional procedures,the webs are usually water-laid upon a suitable web-forming wire. Ineach case the formed web is then passed onto the surface of a heatedrotating drum or series of drums, where it is dried to a suitablemoisture content. The dried web is creped from the surface of the drumby means of suitable creping equipment, usually a creping doctor blade.The dried creped tissue is wound on a suitable drum or reel whichstretches the tissue web as an incident to the winding operation. Theweb is then ready for assembly into finished tissue products. However,in such manufacture of dry creped cellulosic tissue webs certaindifiiculties have been encountered, particularly with respect toadequate release of the webs from the drier section of the tissue-makingapparatus during creping.

In the manufacture of dry creped tissue it is important to obtain aproper amount of adhesion between the web and the drier so that thedesired type of creping results. When there is too little adhesion ofthe web to the drier surface, the web will flare off the drier withoutbeing creped, or will be creped with a coarser type of crepe thandesired, since resistance of the web to removal from the drier surfaceby the creping mechanism is in large part responsible for the type ofcreping effected.

Conversely, if the web adheres too tenaciously to the drier surfaceduring creping, the web may be partially or wholly fractured as anincident to its removal, thereby resulting in a low strength web andrequiring costly slowing down or stoppage of the conventional high-speedtissue-making process. Moreover, it has been found that tightly adheringwebs are often creped more finely than desired, resulting in. otherundesirable physical properties.

It is also desirable to have the creping as uniform as possible acrossthe web, and to avoid various degrees of web adhesion to the driersurface for a particular section of tissue web with consequent unevencreping ofthe web and web areas of differing web strength.

Certain factors have been found to influence the degree of drieradhesion. It has been found, for example, that cellulosic pulps varyconsiderably in their natural adhesivity to drier surfaces when madeinto creped tissue webs. This is due in part to considerable variationsin the concentrations of non-cellulosic constituents. For example, someof these constituents such as pitch aid release, while others such ascarbohydrates increase adhesion.

Sulfate wood pulps and western sulfite wood pulps are particularly proneto cling or stick too firmly to the drier surface to allow easy releasetherefrom. In fact, certain of these pulps have been found to be almostimpossible to utilize commercially in the fabrication of dry crepedtissue webs, without admixture with less strongly adhering pulps.

It has further been discovered that the more highly refined the woodpulp, whatever its origin, the stronger will be the adhesion to driersurfaces of webs fabricated therefrom. Thus, in the manufacture oftissue wadding where the furnish is highly refined, increased drieradhesion normally occurs.

An added difficulty lies in the effect that the water ice utilized inmaking up the stock suspension has on drier adhesion. The stocksuspension, which is the mixture from which the web is made, is anappropriate mixture or suspension of fiber, water and possibly otheradditives. The greater the concentration of certain salts, for examplecalcium salts, in the stock water, the greater the drier adhesionusually encountered.

In addition, various wet strengthresins are utilized in the fabricationof special types of tissue webs, such as are used for paper towels andthe like. These resin usually act as adhesives for the web on the drier,and substantially increase the difiiculty of effecting suitable webrelease from the drier surface.

Attempts to control the degree of adhesion of tissue webs to driersurfaces have comprised adjusting the hardness and pH of the furnish andstock suspension, limiting the use of wet strength adhesive resins,controlling the nature and types of furnishes and using creping aidssuch as glues and soaps in the furnish. However, such attempts have beenexpensive and time consuming, and moreover have not been completelysatisfactory in that controlled web release from the drier surface couldnot always be effected. In this connection, many types of available woodpulps could not be used in the unmodified form for dry creped tissue webmanufacture.

Various soaps and similar release agents which reduce the adhesion oftissue webs to drier surfaces have been added to the stock or furnishbefore fabrication of the tissue webs. Spraying certain types of foamsuppressors on the wire also has some small eiiect on release action.However, addition of such soaps and similar release agents directly tovery dilute furnishes has not proven satisfactory in controlling theadhesivity of certain furnishes to the drier, even when utilized inlarge amounts. Too little of the release agent is generally retained inthe system from the point of addition to the drier surface to beeffective. In addition, this type of control ofdrier adhesion generallyresults in a definite loss of web strength. This loss of web strength isbelieved due to interference by the release agent with properfiber-to-fiber bonding during the formation of the web on theweb-forming Wire.

Use of release agents directly in the stock is further disadvantageoussince these agents tend to accumulate in the stock and build up in thewhite water, so that the degree of drier adhesion cannot be easilycontrolled. In addition, some of these agents have a tendency to foam,clog, and disrupt formation on the tissue-making machinery, and thus tointerfere with the operation of the tissuemaking process. I,

It has now been discovered that the above difficulties can be overcomeand tissue webs having improved characteristics and physical propertiescan be provided by the use of release agents of a specified type andamount at specified points in the tissue-making process. In accordancewith the method of the present invention, the release agents are addedto the tissue-making system after the tissue web has been formed, andprior to or at the entry of the web into a pressure nip which may belocated ahead of or at the point of contact with the drier surface. Themethod of the present invention provides adequate control of drieradhesion and results in'more uniformly creped tissue webs havingincreased web strength and stretchability over conventionally fabricatedcreped tissue Webs. Furthermore, withcertain release agents the webs mayhave certain improved characteristics, for example, increased limpnessand softness. In addition, the tissue webs can be formed from certainwood pulp furnishes hitherto commercially unusable.

'In addition, increased creped tissue web production speed may beobtained by the present process because of reduced energy requirements,that is steam consumption in the drier section of the apparatus. Thiseffect is due primarily to the ability to satisfactorily dry crepe thetissue web at a higher moisture concentration than heretoforeobtainable. In addition, release agents generally reduce surface tensionand allow more water to be removed at the press roll.

In the present process, the drier surface remains cleaner than inconventional processes, due to the fact that the release agents permitthe web to be more cleanly removed in the creping process. Moreover, therelease agents in the present process act as conditioning'agents for theconveyor felts, keeping them in a clean, absorbent, flexible condition.

Accordingly, it is the primary object of the present invention toprovide a faster, more economical method for the manufacture of tissuewebs. It is also an object of the present invention to provide a methodof manufacturing dry creped tissue Webs having increased web strengthand stretchability. It is a further object of the present invention toprovide an improved method for the manufacture of dry creped cellulosictissue webs at a lower breakage frequency. It is also an object of thepresent invention to provide an improved method of controlling drieradhesion through the use of specified release agents on formed tissuewebs. Moreover, it is an object of this invention to provide a methodfor using certain furnishes hitherto considered impractical for use informing dry creped tissue.

Further objects and advantages of the present invention will be apparentfrom a study of the following detailed description and from theaccompanying drawings, of which:

FIGURE 1 is: a schematic representation of the drier section of apapermaking machine arranged for operation in accordance with the methodof the present invention;

FIGURE 2 is an enlarged schematic view of a portion of the drier sectionof a papermaking machine illustrating another method of operation inaccordance with the present invention.

The manufacture ofdry creped cellulosic tissue webs in accordance withthe preferred method of the present invention comprises the steps offorming a web of cellulosic fiber in the conventional manner, adding tothe formed web one or more release agents at a point before a pressurenip and before drying the web, passing the web and release agent througha pressure nip to distribute the release agent uniformly in the web andon a drier surface, drying the web and film of release agent on thedrier, and creping off the dried web from the drier surface.

Normally, the sheet or web is formed by a Water-laying technique on theusual Fourdrinier-type web forming equipment. The mat of fibers of whichthe web is composed is formed by applying to the upper surface of theFourdrinier wire, as by flowing thereon, alayerof stock containing therequired amount of fibers in an amount ofwater which is sufficient toproducetheproper distribution of the fibers in the web, and subsequentlyeliminating a suflicient amount of the water to produce a coherent webor sheet capable of being couched off the end of the wire. p a

For the purposes of the present invention, the fibers used may compriseany cellulosic or other fibers which are adaptable for use in themanufacture of creped webs or sheets of tissue weight. In addition, woodpulp fibers hitherto commercially unusable in dry creping can beutilized in amounts comprising up to 100 percent of the entire furnish.However, the proportions and types of the fibers may be adjusted inaccordance withthe uses to which the creped cellulosic tissue webs orsheets are to be applied. Cellulosicfibers include chemical wood pulpfibers, mechanically produced wood pulp fibers, cotton fibers, etc.Suitable chemical wood pulp fibers include those produced by thesulfite, sulfate, and semi-chemical pulping processes. The fibers may bebleached, but this is unnecessary for the purposes of the presentinvention.

Various synthetic fibers such as rayon, nylon, glass,

polyvinyl chloride, and cellulose acetate fibers may be added in varyingamounts to the furnish to provide webs having certain specificproperties.

The tissue web may be formed on a Fourdrinier webforrning machine havingan open or spout-type headbox or on a cylinder vat machine. An exampleof a Fourdrinier machine is shown in part in FIGURE 1.

As produced on such a machine, the formed cellulosic tissue web normallyhas a moisture content of approxi mately 85 percent by weight at thetime it is couched from the web-forming wire onto the felt. In general,a tissue web useful for purposes of the present invention, should have abasis weight before creping, on a bone dry basis, of between about 3.5and about 15 pounds per ream of 3000 square feet.

Referring now more particularly to FIGURE 1 of the accompanyingdrawings, a wet tissue web 5 after being couched in the usual mannerfrom a web-forming wire 6 is carried by a top felt 7 into the pressurenip between two main press rolls, a top press roll 9 and a bottomsuction press roll 11, and bottom felt 12. The press rolls 9 and 11partially dewater the web 5, reducing the moisture content thereof tobetween about 70 to percent by weight. After the web 5 passes throughthe pressure nip with the top felt 7 it is carried by the top felt 7 Iaround a tail roll 13. During passage of web 5 between the main pressrolls and the tail roll, the web is contacted with a spray of fluidcontaining a release agent. The spray of fluid is delivered to the web 5by a suitable means 15.

The release agent for the purposes of the present invention may he oneor more compounds miscible with water or another volatile carrier. Bymiscible is meant dispersible in or soluble in the volatile carrier. Airalso may be employed as this carrier. The release agent should be suchas to impart a degree of oiliness to steel of less than 0.3 at 20 C.expressed as the coefiicient of friction.

As used herein, the degree of oiliness expressed as the coefii'cient offriction is based on data obtained with a modified Deeley machine usedfor static friction measurements in the commercial testing oflubricants. This machine utilizes two opposing hard steel surfaces, oneprovided by a disc about 4 inches diameter, and the other by three /2inch diameter balls mounted on the underside of a circular carriage andequally spaced around a circle 3 inches in diameter. The carriageengages with a torque measuring device consisting of a coiled springwith an indicating mechanism. The pressure between the engaging surfaceof the plate and the carriage supported balls can be varied by loadingthe carriage with weights. The disc or lower friction surface .is.carried in a bath which contains the lubricant under test, and a gasring is provided under the bath for heating thelubricant, thetemperature being measured by a thermocouple in the bath.

The machine is operated by slowly rotating the disc by means of anelectric motor and gearing. The frictional resistance between thesurfaces causes rotation of the carriage against the action of thespring, and the disc is rotated until slipping of the surfaces occurs,when a pawl-and-ratchet mechanism prevents the spring from unwinding.The torque produced by the spring on the carriage at slip is thus equalto the friction torque and, as the total load is known, the coefficientof friction is thereby obtained. This value is a measure of the boundarylubrication afforded by the substance tested.

The Deeley machine,.the scale of oiliness values and the associated testare described in detail in the Journal of the institute of Petroleum,vol. 26, No. 195, January 1940, pages 1 to 18, A. Fogg and S. A.Hunwicks, The Static Friction of Lubricated Surfaces. Wherever referenceis made to degree of oiliness or coefiicient of friction in thespecification and claims it falls under the above description.

It has'been found that at 20 C. the'oiliness Value or coefllcient offriction for steel on steel is 0.6. With benzene present, the value is0.5, with alcohol 0.42, with trichloroethylene 0.33, and with glycerol0.2. Mineral oils and fatty oils have values in the range from about0.12 to 0.15, while oleic acid has an exceptionally low value of about0.06.

Examples of release agents which are suitable for the purposes of thepresent invention are the following:

Soaps comprising the sodium salts of oleic, stearic, and other fattyacids; emulsified mineral oil; wax emulsions; silicone emulsions;diglycol laurate; polyethylene glycol dilaurate; emulsified fatty acidsof 6 to 18 carbon atom chain'iength, such as oleic, ricinoleic,palmitic, stearic and lauric acids; triethylene glycol; sulfonatedcastor oil; rewetting agents of the fatty ester type, and alkyl arylpolyether alcohols; alkyl ketene dimers, such as the ketene dimer of afatty acid of 12 to 18 carbon atom chain length; softening agents of thesulfonated long chain hydrocarbon type; and, quaternary ammoniumchlorides, such as dihydrogenated tallow di-rnethyl ammonium chloride.

In general, only a relatively minute amount of release sgent compared tothe weight of the web will be necessary to effect the desired controlledrelease of the web from the surface of the drying cylinder. This amountwill depend on the oiliness of the release agent, the type of furnishand weight of the tissue web being released and the temperature of thedried cylinder surface, among other factors. The amount of release agentcan vary as much as 0.01 pound to 25 pounds per ton of finished product,depending on the release agent chosen and the other factors listedabove.

Fatty acids which are liquid at room temperature (65 F.) and which havebetween 14 and 18 carbon atoms in the carbon chain have been found to beparticularly effective release agents, as also are mineral oils utilizedin an oil-in-water emulsion. The former have been successfully utilizedin an amount between .02 and about 2 pounds per ton of tissue web havinga basis weight before creping of about 7.6 pounds per ream of 3000square feet, on a bone dry basis. The latter have been successfullyutilized in an amount between about 1 pound and 21 pounds per ton oftissue web having a basis weight before creping of about 7.6 pounds perream of 3000 square feet, on a bone dry basis.

Since only a relatively minute amount of release agent need be used inachieving effective control of release of the tissue web from the driersurface, as compared with processes where release agents are added tothe furnish, the method of the present invention is relativelyinexpensive. Moreover, increased web yield, strength, stretchability andsoftness in the finished creped tissue web, and increased productionspeed and lower wind breakage frequency render the method of the presentinvention highly desirable.

The selection of the particular release agent may depend not only on itsoiliness value but also on other characteristics of, or imparted by, anyparticular agent,

The release agent in the volatile carrier is applied to the web by aspray boom means 15, in an amount sufficient to spread evenly in the web5 and on its surface when the web 5 is passed through a pressure nip 16between the drying cylinder 17 and the associated rubber covered suctionpress roll 19. The amount of release agent in the carrier should besuiiicient to effect the desired dry creping of the web, as hereinaftermore par ticularly described. The release agent can be applied to theweb 5 at any point prior to the pressure nip'l6. The release agent canalso be applied directly into the pressurenip 16 or the pressure nipbetween the main press rolls. Inasmuch as it is necessary for thepressure nip to spread the release agent evenly in the web, the optimalpoint of application of the release agent will necessarily depend on thetype and amount of release agent and carrier applied, the nature oftheweb, and the rate of the top felt and the web.

The release agent and carrier alternatively may be applied to the topfelt 7 at a point before the pressure nip between the main press rollsor after that pressure nip and before the pressure nip 16. However, whenthe release agent is applied to the top felt 7, it should be appliedsufiiciently far ahead of the pressure nip to allow the release agent tosoak through the felt 7 and reach the surface of the web 5 before theweb and felt enter the pressure nip. Application of the release agent tothe top felt 7 has the advantage of keeping the top felt clean and in aflexible and absorbent condition.

In the apparatus of FIGURE 1, the release agent is applied by a sprayboom 15 having spaced hydraulic spray nozzles directed at the adjacentsurface of the web 5 and extending substantially over the entire widthof the web 5. The boom may, for example, have 0.018 inch spray nozzlesso spaced as to provide a uniform spray over the entire width of the web5. The spray pressure means may be pneumatic as well as hydraulic. Thespray boom 15 is located close to web 5 and between the tail roll 13 andthe main press rolls 9 and 11, as shown in FIGURE 1. Alternatively, itmay be located either prior to the main press rolls, or closer to thepressure nip 16.

Any other apparatus which applies the release agent to the web or,alternatively to the top felt '7, in a controlled amount may be utilizedin the present invention instead of the spray boom 15. For example, arubber printing roll may be used. It has also been found that therelease agent can be successfully applied to the web by means of thebrush roll assembly, as shown in FIGURE 2 of the accompanying drawings.

After the release agent is applied to the web 5, as previouslydescribed, the web Sis carried by the top felt around the tail roll 13and into the pressure nip 16 between the rubber covered suction pressroll 19 and the Yankee drying cylinder 17. The pressure applied at thenip by the press roll 19 spreads and distributes the release agentevenly in the web. It is an important part of the present invention thatthe release agent be uniformly distributed in the web so that it ispresent uniformly on the surface of the web as well. This is to assurean even release of the web from the drier during the subsequent drycreping operation. Such even release of the web accounts for uniformcreping of the tissue web with a dramatically reduced incidence ofbreaks in the web during creping and subsequent stretching andrewinding. In addition, the uniform distribution of the release agent inthe web assures various other advantages of the present invention.

The press roll 19 acts to press the web 5 firmly onto the surface of theYankee drying cylinder 17. That cylinder rotates in a clockwisedirection as viewed in FIGURE 1,

carrying the web 5 with it during rotation. The Yankee drying cylinderis a conventional type of drying means which may be up to 15 feet indiameter. The drying cylinder operatesat an even surface temperaturebetween about 190 F. and about 212 F. and may rotate at speeds up to3000 feet per minute. At this temperature and speed of rotation the webis reduced to a moisture content of between about 3 and about 14 percentby weight before it is creped. Beyond the pressure nip 16, the top felt7 leaves the web 5, and passes around the return roll 21 for reuse inthe processing of tissue web.

After the web 5 is dried on the cylinder 17 to a moisture content ofbetween about 3 and about 14 percent by weight, it is creped off thecylinder by the creping doctor blade 23 and wound onto a reel 24.

The dry creped tissue webs manufactured in accordance with the method ofthe present invention, exhibit increased web tensile strength, havegreater stretchability and have fewer breaks in the subsequent rewindingprocess. In this connection, it has been found that in one typicalprocessing operation with a web formed from a usual type of wood pulpfurnish, the number of breaks per processrewinding may be 25 percentgreater than that of a com-' parable web untreated with release agent inthe manner of the present invention. It is believed the release agentnot only provides effective control of the releasing action of the Webfrom the drier surface, but also lubricates the fiber structure of theformed tissue web, so that the fibers slide over one another moreeasily, or are partially plasticized so that the Web can be stretched toa greater extent without rupturing. An added advantage of the method ofthe present invention is that the creping can be carried out at a highermoisture content than formerly possible, with up to a 10 percent savingin steam requirements for the drying operation. The higher moisturecontent of the tissue web aids in preventing rupturing of the web duringcreping and also during subsequent stretching operations.

With webs fabricated from the usual types of furnishes the desiredrelease of the web from the surface of the drying cylinder duringcreping can be achieved through the use of relatively minute amounts forthe release agent, in accordance with the present invention. The releaseagent in these small amounts has no appreciable effect on the nature ofthe crepe obtained, but significantly reduces the incidence of breaks inthe web during the creping and subsequent rewinding and stretching. Inaddition, effective release from the surface of the drying cylinderduring dry creping of webs fabricated from hitherto commerciallyunusable furnishes can be achieved through the use of release agentsapplied in accordance with the present invention.

It is important to recognize that the present invention is directedprincipally to the dry creping process as distinguished from wet crepingor semi-creping. That is, the web is dried shortly after forming and iscreped directly off the drying cylinder in a continuous process withinthe previously described moisture concentration range, that is betweenabout 3 percent and about 14 percent by weight. In Wet cr ping the sheetis dried almost completely, then is rewetted and reapplied to a drierand crepedtherefrom. In semi-creping the doctor blade is used on a drierusually located about half way along in the drier section and produces aminimum of crepe. The products produced by dry creping differ materiallyfrom those produced by wet creping or semi-creping, both in theirappearance and in their functional characteristics.

FIGURE 2 discloses apparatus for carrying out another method of applyingthe release agent to the web in accordance with the present invention.The release agent is applied directly into the pressure nip 16 between adrying cylinder 17' and associated press 'roll 19'. The web 5 is passedwith a top' felt 7' around a tail roll (not shown) and into the pressurenip 16'. As the top felt 7' and the web 5 enter the pressure nip, 2.release agent in a suitable liquid carrier is sprayed into the pressurenip 16' by any suitable means such as the brush roll means comprising areceptacle 25' which holds the release agent and fluid carrier,anapplicator roll 27, and a brush roll 29. The roll 27 rotates in thereceptacle 25 and picks up therefrom suitable amounts of the releaseagent. The brush roll 29 rotates in a direction counted to the directionof rotation of the applicator roll 27 and is in point contact with therelease agent covered surface of the ro1l'27. The brush roll 29 isequipped with suitable bristles which contact the roll 27 and act tospray a suitable amount of the carrier containing the release agent intothe pressure nip 16', in'an amount sufiicient to assure distribution ofthe release agent in the web and on the surface of the web, and in anamount sufiicient to eifect the desired improved dry creeping of theweb.

As the web 5 containing the release agent is passed with the top felt 7into the pressure nip 16, the pressure exerted by the press roll 19* onthe nip causes the release agent to be distributed evenly within the weband on the surface of the web which contacts the surface of the dryingcylinder 17'. The web 5 and the top felt 7 are separated beyond thepressure nip 16, the web 5 passing onto the surface of the dryingcylinder 17 and the top felt 7' continuing on the surface of the pressroll I? for return for processing of additional tissue web. The web 5'is then subjected to drying and creping, as previously described inconnection with FIG- URE 1.

The modification of the method of the present invention set forth inFIGURE 2 differs from that described in connection with FIGURE 1 only inthat the release agent is applied directly into the pressure nip 16'instead of being applied to the web between the main press rolls and thetail roll. In addition, a brush roll assembly is used to apply therelease agent rather than a spray boom.

It is obvious that a spray boom or other applicating means could be usedin the arrangement of FIGURE 2 instead of the brush roll assembly, andalso that the release agent could be applied to the top felt 7 or to theweb 5' prior to, rather than directly to, the pressure nip 16.. All suchmodifications of the method of the present invention yield quitesatisfactory results with respect to control of drier adhesion and theproduction of improved tissue webs.

The dry creped tissue Web fabricated by the method of the presentinvention, before being incorporated into tissue products, may beexpanded or stretched on any conventional expansion apparatus, such as arewind machine, preferably to within about 20 percent of its totalstretchable length. During expansion, fewer breaks are encountered thanwith conventionally produced webs, due both to the greater strength ofthe web and easier pull out. After expansion, the creped tissue web isready for use in the manufacture of facial tissues, wipes, towels andother tissue products. In this connection, a plurality of webs may beassembled in superposed relation to provide multi-ply, cellulosic tissueproducts- If desired, the plies of web can be bonded together throughthe use of bonding agents and/or embossing or other suitable means.

Illustrative examples of the present invention are set forth as follows:

' Example] A Wood pulp furnish comprised of approximately percentbleached sulfate fibers, the remainder being bleached sulfite fibers,was processed on a commercial tissue-making machine to produce acellulosic tissue web having a basis weight of 7.6 pounds per ream of3000 square feet, on a bone dry basis, before creping. The formed wettissue web was couched off the forming wire onto the top felt. Aftergoing through the main press section it was sprayed with an oil-in-wateremulsion of mineral oil at the rate of 1 pound per ton of the tissueweb, on a bone dry basis, by means of an hydraulic spray boom operatingat 40 pounds pressure. The spray boom had nozzles of 0.018 inch diameterspaced at 3 inch intervals across the width of the web, so as to applyto the web a fairly uniform amount of the mineral oil. The mineral oilused as the release agent in this example was a commercial preparationcalled Cynol 760 produced by the American Cyanamid Company. Thisparticular emulsifiable mineral oil has been treated to induce thereincationic paper softening agent properties and it is normally used as aliquid, light. straw in color and has a specific gravity at .86 at F.and a viscosity of 23 to 28 centipoises at 25 C. It was used as a 0.1percent oil-in-water emulsion. The spray boom was located 10 inches fromthe web, 36 inches from the tail roll between the tail roll and thepress roll associated with a Yankee drying cylinder.

The tissue web carrying the applied mineral oil was then conveyed by thetop felt into the pressure nip between Yankee drying cylinder andassociated press roll. The Yankee drying cylinder had a diameter of 12feet and rotated at a speed of 2300 feet per minute. The temperature ofthis cylinder was maintained between 190 and 200 F. As the web passedthrough the pressure nip the release agent was uniformly spread in thetissue web and on the surface thereof. The web was dried on the dryingcylinder to a moisture content of between about and 7 percent, andcreped off the surface of the drying cylinder with a standard crepingdoctor blade and wound onto the reel at a crepe ratio of about 2.0.

The dry creped tissue web was rewound on a winder which expanded the webuntil it had about 20 percent residual stretch. The expanded web had atensile strength of about 425 grams as opposed to 395 grams tensilestrength in a control product. Moreover, during rewinding the webproduced by the method of the present invention had only 0.3 breaks perton of product as opposed to 1.3 breaks per ton of control product. Thefinished, expanded, dry creped, cellulosic tissue web was very soft andlimp.

Example II A wood pulp furnish comprised essentially of bleached sulfatefibers from southern woods, formerly considered impractical for use inthe manufacture of dry creped tissue under standard operatingconditions, was formed on a conventional paper machine into a cellulosictissue web having a basis weight of 7.6 pounds per ream of 3000 squarefeet, on a bone dry basis, before creping. The formed wet tissue web wascouched off the forming wire onto the top felt and carried through themain press. It was then sprayed with release agent, in this case anoil-in-water emulsion of mineral oil at the rate of 21 pounds per ton oftissue web, on a bone dry basis. A pneumatic spray boom was used forthis purpose, operat ing at 40 pounds air pressure and having nozzleswith an orifice size of .028 inch spaced at 9 inch intervals across thewidth of the web, so as to lay upon the web a fairly uniform dispersionof the release agent. The release agent used in this example was anemulsifia-ble mineral oil sold as a commercial preparation under thetrade name Cynol 760 by the American Cyanam-id Company, having the sameproperties as given in Example I. A 6 percent oil-in-water emulsion wasused.

The spray boom was located 12 inches from the web and between the tailroll and the press roll associated with a Yankee drying cylinder, as inExample I. The tissue web carrying the applied mineral oil was thenconveyed by the top felt into the pressure nip between the Yankee dryingcylinder and associated press roll. The Yankee drying cylinder had adiameter of 12 feet and rotated at a speed of about 1600 feet perminute. The temperature of this cylinder was maintained between 190 and200 5. As the web passed through the pressure nip the release agent wasuniformly spread in the tissue web and on the surface thereof. The webwas dried on the drying cylinder to a moisture content of about 7percent and creped ofi the surface of the drying cylinder with astandard creping doctor blade and wound onto the reel at a crepe ratioof 2.5.

A dry creped sheet tobe used as a control sheet for comparison purposescould not be produced from the same furnish because the excessive driersticking, which occurred when no release agent was present, preventedremoval of a suitable product from the drier.

Example 111 A furnish of chemical wood pulps comprised essentially ofbleached sulfate fibers from West Coast woods, formerly consideredimpractical for use in the manufacture of dry creped tissue, was formedon a conventional paper machine into a cellulosic tissue web having abasis weight of 7.6 pounds per ream of 3000 square feet, on a bone drybasis, before creping. The formed wet tissue was couched off the formingwire onto the top felt and carried through the main press. It was thensprayed with a dilute emulsified fatty acid at the rate of 0.2 pound perton of tissue Web, on a-bone dry basis. A hydraulic spray boom was usedoperating at 55 pounds pressure and having nozzles of 0.018 inchdiameter spaced at 3 inch intervals across the width of the web. Thefatty acid used as the release agent was an unsaturated oleic acidhaving a coeflicient of friction or oiliness value of 0.08 as measuredon the modified Deeley machine. The specific oleic acid used in thisexample is a commercial product called Groco oleic acid and manufacturedby A. Gross and Company. It is white in color and has a titer of 5-8(3., an iodine value of 89-92, free fatty acid content of 99-l00 percentoleic, an acid value of 197-200, a saponification value of 198-201 and amaximum of 1.5 percent unsaponifiables.

The oleic acid emulsion was prepared by mixing 30 gallons of oleic acidwith 30 pounds of Atlox G-2081 (an alkyl aryl sulfonate blended withpolyoxyethylene sorbitan esters of mixed fatty and resin acids)manufactured by Atlas Chemical Company, and 30 gallons of water. Thiswas used in a concentration of about 0.05 percent oleic acid.

The spray boom was located 10 inches from the web and in advance of thetail roll. The tissue web carrying the release agent was then conveyedaround the tail roll and into the nip formed by a press roll and aYankee drying cylinder at a speed of about 2400 feet per minute. Thetemperature of the Yankee drying cylinder was maintained between 190 and200 F. The treated Web was dried to a moisture content of between 4 and6 percent, creped off the Yankee drying cylinder and wound onto the reelat a crepe ratio of 2.3.

As in Example II, a dry creped sheet to be used as a control forcomparison purposes could not be produced from this furnish because asuitable product could not be creped oif the drier when no release agentwas used.

Examples 1, II, and Ill clearly demonstrate the improved resultsobtained by the use of a suitable release agent in accordance with themethod of the present invention. Examples 11 and III show that percentsulfate pulp which had hitherto proved impossible to manufacture into adry creped tissue web by ordinary commercial processes can now be madeinto a high quality creped tissue web in accordance with the method ofthe present invention. That is, the web can be effectively released fromthe drying cylinder with the creping doctor blade when an appropriaterelease agent is applied to the formed web at a point located prior to apressure nip. Reduction in the breakage rate of the web is significantenough to make the the process commercially useful. Moreover, thefinished creped tissue web has a desirable softness and limpness whichmakes it especially suitable for use in facial tissues and other crepedtissue product applications.

In Example I, a creped tissue web, manufactured in accordance with themethod of the present invention, was

compared with a tissue web prepared from the same furnish but withoutthe use of a release agent. The creped tissue web had fewer breaks and acorrespondingly higher overall production speed than the control web.Moreover, the web of the present invention had improved tensilestrength, stretchability, softness and limpness over the control web.

As is seen from the above, adequate control of the release of cellulosictissue webs from the surface of a drying cylinder can be obtainedthrough the application of selected release agents to the formed webs inaccordance with the method of the present invention. Even in cases wheresatisfactory creping results from conventional proc- Yankee type drier.

' economy. The webs so obtained are suitable for use as facial tissues,wiping agents, towels and other creped tissue applications.

The release agents can also be applied to formed cellulosic tissue websor felts prior to pressure nips in accordance with the presentinvention, to achieve certain improved results in the fabrication ofmachine glazed tissue. Such tissue is usually fabricated on conventionaltissue making machinery and is usually glazed on a Adequate control ofrelease of the tissue web from the drier surface Without creping can bereadily achieved through the use of the release agents previouslydescribed herein.

Other suitable modifications of the method of the present invention andthe equipment for carrying out the same, as are within the skill ofthose versed in the art are contemplated as being within the scope ofthe present invention.

I claim:

1. -An improved method of manufacturing dry creped cellulosic tissue,said method including the steps of waterlaying a web of cellulosictissue, reducing the moisture content of said Web to less than about 85%of the weight of the web and eitecting fiber to fiber bonding, applyingto the formed tissue Web before drying a fluid containing a releaseagent, said release agent having an oiliness value of less than 0.3 to20 C. expressed as the coefiicient of friction as obtained on themodified Deeley machine, said release agent being present in saidapplied fluid in an amount of .01 pound to 25 pounds per ton of tissue,said fluid being suflicient to be spread evenly in the web and onthesurface of said web in a pressure nip to control the degree of adhesiveof said web to a drier surface, passing said web together with saidapplied fluid into a pressure nip whereby said release agent is evenlydistributed in said web and on the surface of said web, drying said webon a heated rotating member to a moisture content of between about 3 andabout 14 percent by weight, and creping the dried web from said memberto obtain a creped cellulosic tissue web having improved web strengthand stretchability, said reelase agent substantially retaining itsoiliness during said creping.

2. An improved method of manufacturing dry'creped cellulosic tissue,said method including the steps of waterlaying a web of cellulosictissue, reducing the moisture content of said web to less than about ofthe weight of the web and effecting fiber to fiber bonding, applying tothe formed tissue web before drying a fluid containing mineral oil as arelease agent, said mineral oil being present in said applied fluid inan amount of .01 pound to 25 pounds per ton of tissue, said fluid beingsufi'icient to be spread evenly in the web and on the surface of saidweb in a pressure nip to control the degree of adhesion of said web to adrier surface, passing said web together with said applied fluid into apressure nip whereby said mineral oil is evenly distributed in said Weband on the surface of said web, drying said web on a heated rotatingmember to a moisture content of between about 3 and about 14 percent byWeight, and creping the dried web from said member to obtain a crepedcellulosic tissue web having improved web strength and stretchability,said mineral oil substantially retaining its oiliness during saidcreping.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,637 Montgomery Mar. 24, 1953 1,534,622 Wandel Apr. 21, 1925 1,641,739Cofrin Sept. 6, 1927 1,772,185 Liebeck Aug. 5, 1930 1,863,813 Alden etal. June 21, 1932 1,871,702 Kallander et a1 Aug. 16, 1932 1,958,202Novak May 8, 1934 2,018,244 Alm Oct. 22, 1935 2,030,625 Ellis Feb. 11,1936 2,077,438 Rowe Apr. 20, 1937 2,380,043 Hochwalt July 10, 19452,725,640 Voigtman Dec. 6, 1955 2,819,184 Smith et al. Jan. 7, 19582,940,890 Braun June 14, 1960 2,944,931 Yang July 12, 1960 OTHERREFERENCES Casey: Pulp and Paper, vol. II, 1952, IntersciencePublishers, Inc., N.Y., page 844.

UNITED STATESPATENT. OFFICE CERTIFICATE OF CORRECTION Patent No,$014,832 Decembem: 26, 1961 Harold F, Donnelly e numbered patcertifiedthat error appears in the abov d as It is hereby action and that thesaid Letters Patent should rea ent requiring com" corrected below.

for dried read drier column Column 5 line 29- a line '22, for "85 F,,"read 75 F column 11 line 35 for "to" read at line 41 for "adhesive" readadhesion column 12, line .2 for "'reelase read release Signed and sealedthis 24th day of July 1962.

(SEAL) Attestz' DAVID L. LADD ERNEST W. SWIDER Attesting OfficerCommissioner of Patents

1. AN IMPROVED METHOD OF MANUFACTURING DRY CREPED CELLULOSIC TISSUE,SAID METHOD INCLUDING THE STEPS OF WATERLAYING A WEB OF CELLULOSICTISSUE, REDUCINGG THE MOISTURE CONTENT OF SAID WEB TO LESS THAN ABOUT85% OF THE WEIGHT OF THE WEB AND EFFECTING FIBER TO FIBER BONDING,APPLYING TO THE FORMED TISSUE WEB BEFORE DRYING A FLUID CONTAINING ARELEASE AGENT, SAID RELEASE AGENT HAVING AN OILINESS VALUE OF LESS THAN0.3 TO 20*C. EXPRESSED AS THE COEFFICIENT OF FRICTION AS OBTAINED ON THEMODIFIED DEELEY MACHINE, SAID RELEASE AGENT BEING PRESENT IN SAIDAPPLIED FLUID IN AN AMOUNT OF .01 POUND TO 25 POUNDS PER TON OF TISSUE,SAID FLUID BEING SUFFICIENT TO BE SPREAD EVENLY IN THE WEB AND ON THESURFACE OF SAID WEB IN A PRESSURE NIP TO CONTROL THE DEGREE OF ADHESIVEOF SAID WEB TO A DRIER SURFACE, PASSING SAID WEB TOGETHER WITH SAIDAPPLIED FLUID INTO A PRESSURE NIP WHEREBY SAID RELEASE AGENT IS EVENLYDISTRIBUTED IN SAID WEB AND ON THE SURFACE OF SAID WEB, DRYING SAID WEBON A HEATED ROTATING MEMBER TO A MOISTURE CONTENT OF BETWEEN ABOUT 3 ANDABOUT 14 PERCENT BY WEIGHT, AND CREPING THE DRIED WEB FROM SAID MEMBERTO OBTAIN A CREPED CELLULOSIC TISSUE WEB HAVING IMPROVED WEB STRENGTHAND STRETCHABILITY, SAID REELASE AGENT SUBSTANTIALLY RETAINING ITSOILINESS DURING SAID CREPING.